Note: Descriptions are shown in the official language in which they were submitted.
219729
MLC 2 062
MOLTEN METAL SHAFT AND IMPELLER BEARING ASSEMBLY
Field of the Invention
This invention relates to molten metal pumps. More
particularly, this invention relates to a new and improved shaft
and impeller assembly'for use in molten metal pumps. In
particular, the invention relates to a new and improved means for
attaching a bearing ring to a shaft and/or impeller for use in a
molten metal pump.
The inventive means for attaching a bearing ring to the
shaft and impeller is particularly suited to use in molten metal
circulation, transfer, and gas injection pumps. Throughout the
specification, numerous references will be made to use of the new
design in molten aluminum and zinc pumps, and certain prior art
molten aluminum and zinc pumps will be discussed. However, it
should be realized that the invention could be used in a variety
of molten metal environments wherein a bearing ring is secured to
a rotating shaft or impeller.
Description of the Art
Molten metal pumps are typically comprised of at least
a motor positioned outside of the molten metal environment having
a rotatable shaft extending downwardly into the molten metal. An
impeller is attached to the submerged end of the shaft and is
typically encased in a pump housing. Rotation of the impeller
within the pump housing draws molten metal into an inlet and
forces the molten metal through an outlet. To achieve stable
2197259
rotation of the impeller, the impeller and often the shaft, are
journaled with a bearing against the pump housing and/or
components attached thereto.
Historically, one of the weakest components of a molten
metal pump has been the shaft and impeller assembly.
Particularly, these dXnamic elements of the pump are subjected to
corrosion, oxidation and often ingest large pieces of slag or
dross which impact the impeller and shaft with significant force.
To resist oxidation and corrosion in the high temperature
environment, the shaft and impeller assemblies are typically
constructed of a refractory material such as graphite. However,
graphite is also a soft material which will quickly wear away in
a pump environment. Accordingly, a bearing surface is typically
provided. The bearing surface generally is created by placing a
bearing ring on the impeller and a bearing set on the pump
housing.
Notwithstanding the hostile environment, recent
developments in coupling and drive designs, enhanced shaft to
impeller attachment mechanisms, improved graphite oxidation
resistance and high performance ceramic protection sleeves have
significantly lengthened the life span of the shaft impeller
assembly. Therefore, the attachment of a ceramic bearing ring to
the impeller, and optionally to the shaft, remains one of the
most common points of failure in the entire assembly.
Historically, a bearing ring is cemented to the shaft
and impeller. Particularly, a typical impeller has a generally
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cylindrical portion which is machined to include a
notched periphery, and the bearing ring --often of
silicon carbide-- is cemented into the notch. In certain
designs, the :radially facing wall c:>f the notch has been
canted inwardly, toward the rotational axis, in the
direction of the intersection. with t=he axial facing wall.
However, the prior art designs have remained a frequent
area of failure because the joint is incompletely filled
with cement and the graphite t.o cement adherence is
relatively poor.
To increase the operable life of a molten metal pump
and to increase its overall reliability, it is desirable
in this art to improve the means for attachment of the
bearing ring too the impeller and s~~aft assemblies.
S ummary ~ the Invents~on
o
Accordingly, it is primary c~~bject an aspect
a of of
this invention provide a new and improvedmechanism
to to
secure a bearing to a molten metal. impeller and/or shaft.
It is an advantage of this invention to provide an
improved joint between impeller and bearing ring which
experiences significantly less degradation and/or
breakage.
A still further advantage of this invention is that
the improved joint between the bearing ring and the
impeller and/or shaft is achieved through inexpensive
machining requiring only a simple turning operation.
Additional objects and advantages of the invention
will be set forth in part in the description which
follows and in part
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will be obvious from the description, or may be learned by
practice of the invention. The objects and advantages of the
invention may be realized and attained by means of the
instrumentalities and combinations particularly pointed out in
the appended claims.
To achieve the foregoing objects and in accordance with
the purpose of the invention, as embodied and broadly described
herein, the present invention is comprised of a molten metal
impeller having a body shaped to draw metal through an inlet of a
pump housing and expel molten metal through an outlet of the pump
housing. The impeller includes a bearing adhesively attached to
at least an effective portion of the periphery of the impeller.
The improvement in the design is based upon the inclusion of a
plurality of generally concentric grooves on the surface of the
impeller adjacent the location of the bearing ring. In a
particularly preferred embodiment of the invention, the plurality
of concentric grooves are formed by a single or cooperate set of
spiraling channel(s).
The invention is particularly directed to molten metal
impellers having a generally circular base or top portion
surrounded by a bearing ring and a plurality of vanes extending
from the circular portion. Preferably, the impeller will be
comprised of graphite and the bearing ring comprised of silicon
carbide and the adhesive used to attach the bearing ring to the
impeller is a refractory cement.
In a particularly preferred form of the invention, a
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cylindrical impeller will include a notch having a
radially facing wall and an axially facing wall around
the entire circumference of one end. In a first
embodiment thereof, only the radial:Ly facing wall will
include a plurality of grooves. In a particularly
preferred version, both axial and radial walls will
include grooves. Preferably, these grooves will cover the
entire circumference of the wall. ~>:referably, the grooves
will have a depth in excess of twice the thickness of the
cement joint.
According to an aspect of the present invention,
there is provided a molten metal i.rripeller comprised of a
base portion having vanes extending therefrom, said base
portion including a first generally circular section and
a second generally circular section of a reduced diameter
positioned generally conck=_ntricall.y to the first and
extending therefrom, a circumferential notch being formed
by said first and second sections, said notch having a
generally radial wall formed by said second section and a
generally axial wall. formed by said. first section, at
least one of said radial or axial walls including a
plurality of grooves, said grooves containing a
temperature resistant adhesive joining a bearing ring to
said impeller.
According to another aspect of the present invention
there is provided a molten metal impeller comprised of a
body shaped to draw molten metal through an inlet in a
pumping chamber and expel molten metal through an outlet
in said pumping chamber, a bearing ring cemented to at
least an effective portion of the periphery of said
impeller, wherein the improvement comprises a plurality
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of grooves on a surface of said impeller adjacent the
location of said bearing ring such that tree plurality of
grooves are substantially filled with a cement to secure
said bearing :ring to said impellez:v.
.5 According to yet another aspect of the present
invention there is provided a molten metal impeller
comprised of a generally circular base portion including
a first and second surface and hava.ng vanes extending
radially from said first surface, said circular base
lU portion having a bearing ring adhe~ively attached to a
periphery of Said second surface, raid periphery
including at least one radially facing groove having a
cross-sectional width which is sma:~.ler than a cross-
sectional width of said bearing ring.
15 According to yet another aspect of the present
invention there is provided a molt:~~n metal impeller
comprised of a base portion having vanes extending
therefrom, said base portion including a first generally
circular section and a se~..ond genet:°ally circular section
2U of a reduced diameter positioned generally concentrically
to the first and extending therefrom, a circumferential
notch being formed by Said first and second sections,
said notch consisting of a generally radial wall formed
by said second section and a generally axial wall formed
25 by said first section, at least one of said radial or
axial walls including a plurality of grooves, said
grooves containing a temperature resistant adhesive
joining a bearing ring to said impeller.
Rri Pf l~p~sr_ri~tl0~ the Drawings
The invention consists of the novel parts,
construction, arrangement;, combinations and :improvements
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shown and described. The accompanying drawings, which are
incorporated in and constitute a part of the
specification illustrate one emboc~~_ment of the invention,
and together with a description, serve to explain the
principals of the invention. O.f the drawings:
Figure 1 is a diagrammatic view of a molten metal
pump for which the inventive impeller and shaft design is
suited;
Figure 2 is an elevation view, partially in section,
of an alternative molten metal pump for which the present
invention impeller design is suited;
Figure 3 is a perspective view of a impeller and
shaft assembly, generally of the type in Figure 1,
incorporating the inventive beariry joint;
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Figure 4 is a perspective view of an alternative
impeller and shaft assembly, generally of the type in Figure 2,
incorporating the inventive bearing joint;
Figure 5 is a partial elevation view of the impeller of
Figure 4 having the bearing ring removed;
Figure 6 is,a partial elevation view of the impeller of
Figure 3 having the bearing ring removed;
Figure 7 is a cross-sectional view of the impeller of
Figure 3; and
Figure 8 is a cross-sectional view of the impeller of
Figure 4.
Detailed Description of the Invention
Reference will now be made in detail to the present
preferred embodiments of the invention, examples of which are
illustrated in the accompanying drawings.
While the invention will be described in connection
with preferred embodiments, it will be understood that it is not
intended to limit the invention to those embodiments. On the
contrary, it is intended to cover all alternatives, modifications
and~equivalents that may be included within the spirit and scope
of the invention defined by the appended claims.
Referring now to Figure 1, a typical molten metal pump,
in this instance a gas injection pump, for which the present
inventive bearing joint is suitable is depicted. The pump is
generally comprised of a hanger/motor mount assembly 1 and a
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motor 3. The motor mount 1 is secured to posts 5, comprised of a
refractory material, by a plurality of sockets 7 and bolts 9.
The motor is secured to refractory shaft 11 by a coupling
assembly comprised of motor coupling 13, universal joint 15 and
shaft coupling 17. Posts 5 are secured to pump housing 19 by
refractory cement and shaft 11 extends into pumping chamber 21
thereof. Shaft 11 is secured to a molten metal impeller 23
rotatable within pumping chamber 21. Pump housing 19 includes a
shaft bearing mount with bearing set 25 and a base bearing set
27. In an assembled form, bearing ring 29 on the shaft and
bearing ring 31 on the impeller are journaled by shaft bearing
set 25 and base bearing set 27 respectively to secure the shaft
and impeller during high speed rotation.
During rotation of impeller 23, molten metal is drawn
into pumping chamber 21, in this instance, through the top and
discharged through snout 33 of pump housing 19. Since the pump
has a top inlet, a baffle plate 43 is included to reduce the
likelihood of ingestion of solid objects which could clog or
destroy the rotating impeller. As stated, the molten metal pump
depicted in Figure 1 is a gas injection model, and therefore
includes injection tube plug 35, injection tube 37, injection
tube nipple 39 and injection tube clamp 41.
Figure 3 generally depicts the impeller of the type
shown in Figure 1, wherein shaft 11, including bearing 29, is
secured to impeller 23, including bearing ring 31.
Referring now to Figure 2, an alternative type of
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molten metal pump, in this case a circulation pump, is depicted.
In this instance, impeller 51 is a bladed impeller attached to
shaft 50 and includes a bearing ring 53 secured to the periphery
of its base portion, opposed by bearing set 54. Figure 4
generally depicts the impeller of the type shown in Figure 2,
wherein shaft 50 is secured to impeller 51 having bearing ring
53.
Referring now to Figure 5, the notch 56 of impeller 51
which accommodates a bearing ring (not shown) is depicted.
Impeller 51 includes a base portion 55 and a plurality of vanes
57 extending therefrom. The generally circular base 55 includes
peripheral notch 56 at its lower most portion and is sized
appropriately to accommodate a bearing ring (not shown).
Radially facing wall 59 of the notch and axially facing wall 61
of the notch include a plurality of grooves 58, however, the
inventive design includes an impeller having only one grooved
wall.
It has been found that the grooved walls facilitate
even disbursement of a cement, for example FraksetTM cement
available from Metaullics Systems, Co. L.P., over th.e entire
joint surface. In addition, the grooved graphite surface
provides improved mechanical bonding at the graphite/refractory
cement interface.
As noted earlier, the impeller/bearing ring joint has
been a persistent problem in operation of metal pumps. However,
the inventors have found that securing a bearing ring to a~
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impeller in the fashion described herein surprisingly results in
a bearing r-ing which cannot be removed --after cement curing--
through repeated striking with a hammer. Moreover, striking of
an impeller/bearing arrangement constructed in accord with the
inventive design usually results in only chipping of the bearing
ring and no cracking of the cement joint.
Referring now to Figure 6, impeller 23 and shaft 11 are
depicted. In this instance, the impeller includes a base portion
24, generally circular in shape, having a bird cage structure
with a plurality of vanes 72 separated by oval .passages 74,
extending perpendicular therefrom. Again, the impeller base 24
includes a notch 26 at its lower most periphery. More
particularly, notch 26 is formed by a radial wall 28 and an axial
wall 30, each having grooves 32. In this embodiment, as opposed
to the embodiment of Figure 5 wherein a plurality of concentric
grooves are formed, the grooves of Figure 6 are formed as a
single spiraling channel_ Importantly, when cement is placed an
the grooved surface and the impeller fitted thereto, rotation of
the impeller results in "pumping" of the cement throughout the
joint. Moreover, a clockwise rotation of the impeller in
combination with the spiraling groove 32 results in a pumping of
the cement inwardly along radial face 30 and downwardly along
axial face 28.
Figure ? depicts the impeller of Figure 6 wherein a
grooved surface 34 is formed on shaft 11 and filled by cement 36
to secure bearing ring 29 thereto. Referring to impeller 23,
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cement 36 forms a joint 42 with bearing ring 31. Preferably, the
grooves 32 have a depth in excess of the thickness of joint 42,
more preferably at least twice the depth of the joint thickness.
With reference to Figure 8, bearing ring 53 is secured by cement
36 creating a joint 42 with impeller 51.
The invention is not limited to the impeller designs
depicted herein. Moreover, the invention is envisioned as being
suited to any molten metal impeller design wherein a bearing is
secured to the impeller. For example, the impellers and pumps
disclosed in United States Patents 3,836,280; 5,028,211;
4,786,230; 5,203,681; 5,470,201; 5,078,572; 2,948,524; 3,048,384;
4,940,384 would benefit from the inventive joint design disclosed
in those patents.
Accordingly, the skilled artisan will note that the invention is
not limited to a particular impeller design. Rather, the
invention is directed to a mechanism for attachment of a bearing
material to a molten metal impeller of any design.
Thus, it is apparent that there has been provided, in
accordance with the invention, a molten metal impeller and/or
shaft bearing joint that fully satisfies the objects; aims and
advantages set forth above. While th.e invention has been
described in conjunction with the specific embodiments thereof,
it is evident that many alternatives, modifications, and
alternatives will be apparent to those skilled in the art in
light of the foregoing description. Accordingly, it is intended
to embrace all such alternatives, modifications and variations as
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fall within the spirit and broad scope of the appended claims.
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